Real Dictionary

functionalism
uncountable noun: Functionalism is the idea that the most important aspect of something, especially the design of a building or piece of furniture, is how it is going to be used or its usefulness.

functionalism in American English
the theory or practice in art, architecture, and design that the structure or design of anything should be strongly related to its function
noun: a design movement evolved from several previous movements or schools in Europe in the early 20th century, advocating the design of buildings, furnishings, etc., as direct fulfillments of material requirements, as for shelter, repose, or the serving of foo

functionalism in British English
noun: the theory of design that the form of a thing should be determined by its use